The purpose of ths study is to measure the hypothalamic-pituitary- adrenal axis (HPA) axis function and the hippocampus in women with Posttraumatic Stress Disorder (PTSD) related to childhood sexual abuse. The study will entail measurement of hippocampal volume with MRI, assessment of memory function with neuropsychological testing, 24 hour measurement of plasma cortisol, ACTH and Beta-endorphin, a CRF and ACTH challenge test and administraion of dexamethasone with measurement of memory function.